From time to time in the past, there has been interest in reducing wastage of hydrocarbon fuels such as gasoline, primarily as an economy measure. Recently, however, there has been renewed interest in reducing such wastage, to avoid polluting the atmosphere, and more recently, because of the actual shortages of gasoline and other fuel and their rising costs, to save fuel. For these reasons, an objective, as to gasoline for example, is to restrict the emission of hydrocarbonaceous materials from the gasoline into the atmosphere.
The emission of hydrocarbons from gasoline into the atmosphere can be divided into two categories: (1) emissions from incomplete combusion in the operation of motor vehicles and (2) emissions in the handling of the gasoline before the combustion process occurs. From the following data, the relative magnitude of each category can be appreciated.
The Environmental Protection Agency gives an average figure of hydrocarbon emission from incomplete combustion of 200 pounds per 1,000 gallons of gasoline consumed in a vehicle with no control devices. U.S. federal New Car Emission Standards adopted for the 1975 model year require that emissions not exceed 0.46 grams per mile. Using the average mileage figure of 14.4 miles per gallon, this emission limit is equivalent to 14.6 pounds per 1,000 gallons. Information currently available indicated that further reductions in this category are not economically feasible.
A study of the typical pattern of gasoline storage and handling reveals five major points of hydrocarbon emission before the combustion process occurs: (a) Breathing and filling losses from storage tanks at refineries and bulk terminals; (b) Filling losses from loading tank trucks at refineries and bulk terminals; (c) Filling losses from loading underground storage tanks at service stations; (d) Spillage and filling losses in filling automobile gas tanks at service stations; and (e) Evaporation losses from the carburetor and gas tank of motor vehicles.
Breathing loss has been defined as the loss associated with the thermal expansion and contraction of the vapor space resulting from temperature cycles. Filling loss has been defined as the loss due to vapors being expelled from a tank by displacement as a result of filling.
In "splash filling," the gasoline enters the top of the fill pipe and then has a free fall to the liquid surface in the tank. The free falling tends to break up the liquid stream into droplets. As these droplets strike the liquid surface, they carry entrained air into the liquid and a kind of boiling action results as this air escapes up through the liquid surface. The net effect of these actions is the creation of additional vapors in the tank. In "submerged filling," the gasoline flows to the bottom of the tank through the fill pipe and enters below the surface of the liquid. This method of filling creates very little disturbance in the liquid bath and, consequently, less vapor formation than splash filling.
The following table is from data from the publication "Compilation of Air Pollutant Emission Factors" -999-AP-42 published by the U.S. Environmental Protection Agency.
______________________________________ Hydorcarbon Emissions Point of emission lb/1000 gal. of throughput ______________________________________ Filling tank vehicles Splash filling 8.2 Submerged filling 4.9 50% splash filling and 50% submerged filling 6.4 Filling service station tanks Splash filling 11.5 Submerged filling 7.3 50% splash fill and 50% submerged filling 9.4 Filling automobile tanks 11.6 Automobile evaporation losses 92 (gas tank and carburetor) ______________________________________
From the above data, it can readily be seen that emissions from filling are a significant problem.
It is also known that in the standard rigid steel automotive gasoline tank, there is a substantial amount of "sloshing" of the fuel as the vehicle moves. This results in a kind of "boiling" action similar to that described above as being experienced with "splash filling." The result is that a substantial amount of gasoline vapor is constantly being generated within the tank, and the amount of vapor so generated becomes increasingly substantial as the level in the tank drops from the completely full condition as more space becomes available. This phenomenon increases any given fuel level to a point where the atmosphere immediately above the gasoline becomes saturated. To maintain such a saturated condition, however, is made more difficult if not impossible by the practice of "venting," that is, in the past provision has been made to permit pressure differentials between the interior and the exterior of the tank to be relieved. This is necessary because the volume increases due to vaporization of the fuel from "sloshing" or temperature rises could otherwise become so substantial as to cause the tank to burst. Conversely, as "sloshing" subsides, and/or temperature drops, and/or gasoline is removed from the tank the resulting vacuum within the tank can become so substantial as to cause the tank to buckle. The usual method of coping with these considerations in the past has been to vent the tank to the atmosphere, but the result of this has been a signicant amount of "breathing," and consequent loss of the lowest boiling point constituents of the gasoline, which are valuable energy sources and are believed to be potent as chemical causes and reactants to produce objectionable environmental contamination and conditions such as the well-known California "smog."
In the past, various attempts have been made to inhibit such fuel loss and/or contamination phenomena. Some of the devices which have been suggested for coping with these problems have included floating a slab of plastic or foam rubber on the surface of the fuel, and the use of a vacuum relief valve and a pressure relief valve in the tank. In this connection reference is made to Shiobara U.S. Pat. No. 3,653,537. Such suggestions have had limited acceptance, however, due to their comparatively complex structure and limited effectiveness.
Accordingly, it is an object of the present invention to provide a means to decrease the loss of vapors from vehicular fuel storage systems to the atmosphere.
It is another object of the present invention to provide a means for decreasing the loss of vapors from vehicular fuel storage systems which is simple in structure, functionally reliable and effective, and inexpensive to produce and maintain.